System for changing location registration

ABSTRACT

A mobile terminal, which is registered to either a first mobile communication network or a second communication network, determines whether it is possible to register to the first mobile communication network on the basis of control information received from the second mobile communication network. Then, the mobile terminal attempts to register to the first mobile communication network a predetermined number of times in a case that it is determined that it is possible to register to the first mobile communication network.

This application is a continuation of U.S. patent application Ser. No.10/828,977, filed Apr. 21, 2004, now U.S. Pat. No. 7,386,312 whichclaims the benefit of the filing date under 35 U.S.C. §119(a)-(d) toJapanese Application Serial. No. JP 2003-117107, filed Apr. 22, 2003,all of which are incorporated by reference.

BACKGROUND

1. Technical Field

The present invention relates to techniques for carrying out locationregistration to a plurality of mobile communication networks.

2. Related Art

In recent years, a number of third generation mobile communicationnetwork systems, such as W-CDMA (Wideband Code Division Multiple Access)cdma 2000(Code Division Multiple Access 2000) have been provided. Unlikesecond generation mobile communication network systems, such asGSM(Global System for Mobile Communications), third generation mobilecommunication network systems can provide such services as high-speeddata communication, or international roaming. However, service areas formobile communications of a third generation system are smaller thanthose for mobile communications of a second generation system;therefore, it is common for a third generation system user to registerhis/her own mobile terminal to a mobile communication network of asecond generation system in a case that a mobile communication networkof a third generation system is not available.

To overcome the above problems, Patent Publication 1(JP2002-535902corresponding to U.S. Pat. No. 6,594,242) discloses techniques to enablea user of a mobile terminal to switch from a mobile communicationnetwork of a third generation system to that of a second generationsystem. A base station belonging to a mobile communication network of athird generation system transmits to a mobile terminal when the mobileterminal is within range of a base station of a mobile communicationnetwork of a second generation system, control information includingchannel information specifying a base station belonging to the networkof the second generation system. Then, the mobile terminal specifiesconnects to an available base station belonging to a mobilecommunication network of the second generation system on the basis ofthe channel information included in the above control information.Accordingly, a mobile communication network to which a mobile terminalis connected is changed from a mobile communication network of a thirdgeneration system to a mobile communication network of a secondgeneration system.

Where both second and third generation mobile communication systems areavailable, it is preferable to use a mobile communication service of athird generation system, since a third generation system has theabove-described merits in comparison with a second generation system. Inone method for using a third generation system by priority, a mobileterminal executes the following operations: A mobile terminal, standingby for a call in a mobile communication network of a second generationsystem, cancels its standby status periodically, and detects locationinformation transmitted from a mobile communication network of a thirdgeneration system. Then, the mobile terminal is registered to a mobilecommunication network of a third generation system if such locationinformation is detected.

However, when in the process of detecting location informationtransmitted from a mobile communication network of a third generationsystem, a user of a mobile terminal cannot answer an incoming call viathe mobile communication network of the second generation system. Thatis to say, if the mobile terminal is registered to a mobilecommunication network of a third generation system without anyrestrictions, it is difficult to call a mobile terminal via a mobilecommunication network of a second generation system. Further, ascompared with standing by for a call, location registration uses moreelectric power. From this point of view, it is not satisfactory to beregistered to a mobile communication network of a third generationsystem without any restrictions.

DISCLOSURE OF INVENTION

To overcome the above problems, the present invention has an object ofproviding techniques for registering a mobile terminal to a first mobilecommunication terminal by priority without disturbing communicationperformed via a second mobile communication network.

To solve the above problems, the present invention provides a mobileterminal comprising communication means having a communication functionfor using a first mobile communication network and a second mobilecommunication network; determination means for determining, when themobile terminal is registered to the second mobile communicationnetwork, whether it is possible to register to the first mobilecommunication network, on the basis of notification informationtransmitted from the second mobile communication network; and attemptmeans for attempting, in a case that it is determined that it ispossible to register to the first mobile communication network, toregister to the first mobile communication network.

Further, the present invention provides a communication systemcomprising a first mobile communication network; a second mobilecommunication network having a base station for transmittingnotification information indicating that it is possible to register tothe first mobile communication network; and a management device, inaccordance with location registration of a mobile terminal to either thefirst mobile communication network or the second mobile communicationnetwork, for storing data in correlation with a identifier of the mobileterminal, the data indicating a mobile communication network to whichthe mobile terminal is registered.

Further, the present invention provides A location registration changingmethod comprising a first step of determining in a mobile terminalwhether it is possible to register to a first mobile communicationnetwork on the basis of notification information received from a secondmobile communication network, the mobile terminal having a communicationfunction for using the first mobile communication network and the secondmobile communication network; a second step of transmitting from themobile terminal to the first mobile communication network, anotification including an identifier, in a case that the determinationis positive; and a third step of receiving in a management device anotification transmitted by the mobile terminal in the second stepthrough the first mobile communication network, and storing in themanagement device data indicating that the mobile terminal is registeredto the first mobile communication network, the mobile terminal beingspecified by an identifier included in the notification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram indicating an example of the overall configurationof a communication system according to the present invention.

FIG. 2 is a diagram explaining a relationship between a service area 100of a first mobile communication network 10, a service area 200 of asecond mobile communication network 20, a location registration area210A, and a location registration area 210B.

FIG. 3 is an example of registration possibility information transmittedfrom a base station 21 A and a base station 21 B.

FIG. 4 is an example of a location registration management table storedin a management device 60.

FIG. 5 is a diagram explaining an example of the configuration of amobile terminal 50.

FIG. 6 is a flowchart indicating a flow of the operation when a controlunit 510 of mobile terminal 50 is turned on.

FIG. 7 is a flowchart indicating a flow of an operation when controlunit 510 of mobile terminal 50 stands by for a call in a first mobilecommunication network.

FIG. 8 is a flowchart indicating a flow of an operation when a controlunit 510 of mobile terminal 50 stands by for a call in a second mobilecommunication network.

FIG. 9 is a diagram explaining a relationship between service area 100and a location registration area 210C.

BEST MODE FOR CARRYING OUT THE INVENTION A. Configuration

<1. Configuration of a Communication System>

FIG. 1 is a diagram indicating an example of the overall configurationof a communication system according to the present invention. As shownin FIG. 1, a first mobile communication network 10 and a second mobilecommunication network 20 are connected to a fixed telephone line 40through a gateway exchange device 30. In this embodiment, first mobilecommunication network 10 is a mobile communication network of a W-CDMAsystem, and second mobile communication network 20 is a mobilecommunication network of a PDC system. Hereafter, a service area offirst mobile communication network 10 is referred to as “service area100”, and a service area of second mobile communication network 20 isreferred to as “service area 200”. As shown in FIG. 2, service area 200covers service area 100. In this embodiment, a case will be describedwhere service area 200 covers the whole of service area 100, however, itis also possible that service area 200 covers a part of service area100. Further, in this embodiment, first mobile communication network 10is a W-CDMA system, and second mobile communication network 20 is a PDCsystem; however, first mobile communication network 10 may be a mobilecommunication network of a cdma 2000 system, and second mobilecommunication network 20 may be a mobile communication network of aGSM(Global System for Mobile Communication) system. That is to say, anycombination of systems is possible, provided that a system of firstmobile communication network 10 is different from a system of firstmobile communication network 20.

First mobile communication network 10 includes base station 11 andlocation management device 12. A radio area is formed with base station11 at its center, and base station 11 executes radio communication witha mobile phone of a W-CDMA system. For the sake of explanation, in FIG.1, only one base station is indicated, but there are in fact a number ofbase stations in first mobile communication network 10. Service area 100of first mobile communication network 10 is divided into a plurality oflocation registration areas, and there are a number of base stations inone location registration area. By transmitting to a mobile phonenotification information including information specifying a locationregistration area (hereafter, referred to as “location information”),each base station notifies its location information to a mobile phone. Amobile phone can be registered to first mobile communication network 10by storing, in location management device 12, location informationcorrelating with a terminal identifier (e.g. a telephone number assignedto a mobile phone) specifying a mobile phone. That is to say, locationmanagement device 12 manages a location registration area in which amobile phone, being registered to first mobile communication network 10and using a mobile telephone service, is located.

As shown in FIG. 1, second mobile communication network 20 includes abase station 21A and a base station 21B, and location management device22. Hereafter, it is referred to as “base station 21” except where it isnecessary to distinguish base station 21A and base station 21B. A radioarea is formed with base station 21 at its center, and base station 21executes radio communication with a PDC mobile phone in radio area.There are two base stations in FIG. 1; however, there are actually alarger number of base stations. A service area 200 of second mobilecommunication network 20 is divided into a plurality of locationregistration areas in the same manner as that of first mobilecommunication network 10, and there are a plurality of base stations inone location registration area. In this embodiment, base station 21A isin location registration area 210A, and base station 21B is in locationregistration area 210B.

Base station 21 transmits to a mobile phone in radio area formed by basestation 21, notification information including location information of alocation registration area to which base station 21 belongs.Additionally, base station 21 transmits to a mobile phone, information(hereafter referred to as “registration possibility information”)indicating whether it is possible to be registered to first mobilecommunication network 10, a mobile phone in a location registration areato which base station 21 belongs, along with the above notificationinformation. As shown in FIG. 3, registration possibility information is2-bit information having a bit pattern of either “00” or “01”. A bitpattern “00” indicates that it is impossible for a mobile phone to beregistered to first mobile communication network 10, and a bit pattern“01” indicates that it is possible for a mobile phone to be registeredto first mobile communication network 10. For example, base station 21Atransmits to a mobile phone, notification information includingregistration possibility information whose bit pattern is “01”, and basestation 21 b transmits to a mobile phone, notification informationincluding registration possibility information whose bit pattern is“00”. This is because location registration area 210A to which basestation 21A belongs is within service area 100, and locationregistration area 210B to which base station 21B belongs is outsideservice area 100.

On the other hand, a mobile phone to which registration information istransmitted from base station 21 can be registered to second mobilecommunication network 20 in the same manner as that of first mobilecommunication network 10. That is to say, location management device 22manages location registration areas in which a mobile phone, beingregistered to second mobile communication network 20 and using a mobiletelephone service, is located.

A mobile terminal 50 is a mobile phone being registered to either firstmobile communication network 10 or second mobile communication network20, and standing by for a call. More specifically, mobile terminal 50stores a terminal identifier for specifying mobile terminal 50, and isregistered to first mobile communication network 10 by storing inlocation management device 12, a terminal identifier correlated withlocation information transmitted from base station 11. Further, mobileterminal 50 is registered to second mobile communication network 20 bystoring in location management device 22, a terminal identifiercon-elated with location information transmitted from base station 21.Additionally, mobile terminal 50 changes location registration area ofmobile terminal 50 from first mobile communication network 10 to secondmobile communication network 20, or from second mobile communicationnetwork 20 to first mobile communication network 10. Then, mobileterminal 50 notifies a management device 60 that mobile terminal 50 isnewly registered to first mobile communication network 10 or secondmobile communication network 20, or is registered to first mobilecommunication network 10 from second mobile communication network 20 orthe other way around.

Management device 60 is a computer device connected to first mobilecommunication network 10 and second mobile communication network 20, andstores a location registration management table as shown in FIG. 4. Alocation registration management table stores a terminal identifier ofmobile terminal 50 in correlation with a registration section. Aregistration section contains the information specifying a mobilecommunication network to which mobile terminal 50 is registered andstands by for a call. In this embodiment, a registration section has avalue of either “1” or “0”. “1” indicates that mobile terminal 50 isregistered to first mobile communication network 10 and stands by for acall, and “0” indicates that mobile terminal 50 is registered to secondmobile communication network 20 and stands by for a call. Also,management device 60 updates the contents of a location registrationmanagement table on the basis of notifications transmitted from mobileterminal 50. In this manner, management device 60 ensures that eithermobile terminal 50 is registered to first mobile communication network10 and stands by for a call or, mobile terminal 50 is registered tosecond mobile communication network 20 and stands by for a call.Hereafter, writing in a location registration management table isreferred to as “activating a mobile communication network”, a terminalidentifier of mobile terminal 50 correlated with a registration section.In this manner, mobile terminal 50 is able to use a voice communicationservice through a mobile communication network to which mobile terminal50 is registered by activating a mobile communication network. Morespecifically, for example, when mobile terminal 50 is called by atelephone connected to fixed telephone line 40, gateway exchange device30, which has received a call from the above telephone, specifies amobile communication network to which mobile terminal 50 is registeredby referring to a location registration management table. Then, mobileterminal 50 is called in the standard call process manner.

<2. Configuration of Mobile Terminal 50>

Next, the configuration example of mobile terminal 50 will be describedwith reference to FIG. 5. As shown in FIG. 5, mobile terminal 50 iscomprised of control unit 510, display unit 520, operation unit 530,communication unit 540, storing unit 550, and bus 560 which connectseach unit.

Control unit 510 is, for example, CPU (Central Processing Unit), and tocontrol each unit of mobile terminal 50 by executing software stored instoring unit 550.

Display unit 520 is, for example, a crystal display and a drive circuit,and displays images in compliance with image information transmittedfrom control unit 510. Operation unit 530 has a plurality of operationalidentifiers input by users such as numbers, letters, or instructions,and provides to control unit 510, information in compliance withoperational identifiers.

Communication unit 540 is comprised of a first communication interface(hereafter, referred to as “IF”) unit 541, a second communication IFunit 542, and an antenna 543. First communication IF unit 541 receivesinformation transmitted from base station 11 via antenna 543, andprovides the received information to control unit 510. Also, firstcommunication IF unit 541 transmits to base station 11 via antenna 543,information transmitted from control unit 510. Second communication IFunit 542 receives information transmitted from base station 21 viaantenna 543, and provides the received information to control unit 510.Also, second communication IF unit 542 transmits to base station 21 viaantenna 543, information transmitted from control unit 510.

Storing unit 550 has a volatile storing unit 551 and a nonvolatilestoring unit 552. Volatile storing unit 551 is, for example, RAM (RandomAccess Memory) and is used as a work area by control unit 510 runningsoftware. Nonvolatile storing unit 552 is configured by EEPROM(Electrically Erasable Programmable Read Only Memory) and ROM (Read OnlyMemory). A network flag, specifying a mobile communication network towhich mobile terminal 50 is registered, is written in EEPROM. A networkflag has a value of “1” and “0”, and “1” indicates that mobile terminal50 is registered to first mobile communication network 10, and “0”indicates that mobile terminal 50 is registered to second mobilecommunication network 20. The above-described location information iswritten in EEPROM. On the other hand, the above terminal identifiers, OS(Operating System) software, and communication control software arewritten in ROM. The functions provided to control unit 510 by executingsoftware will be described.

For example, when a user pushes a power button (not shown in FIG. 5) ofoperation unit 530 to turn on mobile terminal 50, control unit 510 readsout and executes OS software from ROM. The functions for controllingeach unit of mobile terminal 50, or for executing other software areprovided to control unit 510 running OS software. Then, control unit510, operating OS after loading OS software, reads out and executescommunication control software from ROM. The two functions, unique to amobile terminal according to the present invention, are provided tocontrol unit 510 being operated in compliance with communication controlsoftware.

A first function is to register mobile terminal 50 to either firstmobile communication network 10 or second mobile communication network20, and activate a mobile communication network to which mobile terminal50 is registered. A second function is to change a mobile communicationnetwork in which mobile terminal 50 is registered, and notify managementdevice 60 that a mobile communication network in which mobile terminal50 is registered is changed. Specifically, when control unit 510 detectsthat mobile terminal 50 being registered in first mobile communicationnetwork 10 and standing by for a call, moves outside service area 100,control unit 510 changes location registration of mobile terminal 50 tosecond mobile communication network 20 in compliance with a flowchart inFIG. 7, and activates second mobile communication network 20. Also,control unit 510, being registered in second mobile communicationnetwork 20 and standing by for a call, determines whether mobileterminal 50 can be registered to first mobile communication network 10in compliance with a flowchart in FIG. 8. Then, it is determined thatregistration is possible, control unit 510 attempts to change locationregistration of mobile terminal 50 to first mobile communication network10, and activates first mobile communication network 10 in a case thatmobile terminal 50 is registered to first mobile communication network10 successfully.

As described above, in a case that mobile terminal 50 can be registeredto either first mobile communication network 10 or second mobilecommunication network 20, a function for registering mobile terminal 50to first mobile communication network 10 by priority is provided tocontrol unit 510 operated in accordance with communication controlsoftware.

B. Operation

Here, the operation example of a communication system will be describedaccording to the present invention. It is assumed that a user of mobileterminal 50 moves to a location registration area 210B after mobileterminal 50 is turned on in location registration area 210A. Then, auser of mobile terminal 50 moves from location registration area 210B tolocation registration area 210A.

<1. Operation at the Time when Mobile Terminal 50 is Turned On>

Firstly, the operation of mobile terminal 50 will be described withreference to FIG. 6 at the time of when mobile terminal 50 is turned onin location registration area 210A. FIG. 6 is a flowchart indicating anoperational flow performed by control unit 510. As shown in FIG. 6,control unit 510 determines whether mobile terminal 50 can be registeredto first mobile communication network 10(Step SA1). Specifically,control unit 510 determines that mobile terminal 50 can be registered tofirst mobile communication network 10 in a case that control unit 510receives notification information, transmitted from base station 11,through first communication IF unit 541.

In a case that the determination result in Step SA1 is “Yes”, controlunit 510 registers mobile terminal 50 to first mobile communicationnetwork 10 (Step SA2). Specifically, control unit 510 writes in storingunit 550, location information included in notification informationreceived in step SA1. Then, control unit 510 generates a communicationmessage (hereafter, referred to as “location registration message”)requesting to store in location management device 12, locationinformation and a terminal identifier stored in storing unit 550, andtransmits a location registration message to location management device12.

Then, control unit 510 activates first mobile communication network 10(Step SA3). Specifically, control unit 510 sets a network flag stored instoring Unit 550 to “1”, and transmits to management device 60 throughfirst communication IF unit 541, a communication message(hereafter,referred to as “activation message”) including a terminal identifier anda control code for activating first mobile communication network 10.Hereafter, control unit 510 operates the process (a first stand by forprocess) shown in a flowchart of FIG. 7.(Step SA4).

In a case that the determination result in Step SA1 is “No”, controlunit 510 determines that mobile terminal 50 can be registered to secondmobile communication network 20 (Step SA5). Specifically, control unit510 determines that mobile terminal 50 can be registered to secondmobile communication network 20 in a case that control unit 510 receivesnotification information, transmitted from base station 21, throughsecond communication IF unit 542. In this manner, it is firstlydetermined whether mobile terminal 50 can be registered to first mobilecommunication network 10, and then it is determined whether mobileterminal 50 can be registered to second mobile communication network 20only after it is not possible to be registered to first mobilecommunication network 10; this is because mobile terminal 50 is to beregistered to first mobile communication network 10 by priority.

In a case that the determination result in Step SA5 is “Yes”, controlunit 510 registers mobile terminal 50 to second mobile communicationnetwork 20 (Step SA6). Specifically, control unit 510 writes in storingunit 550, location information included in notification informationreceived in step SA5. Then, control unit 510 generates a locationregistration message including location information and a terminalidentifier stored in storing unit 550, and transmits it to locationmanagement device 22 through second communication IF unit 542.

Then, control unit 510 activates second mobile communication network 20(Step SA7). Specifically, control unit 510 sets a network flag stored instoring unit 550 to “0”, and transmits to management device 60 throughsecond communication IF unit 542, an activation message including aterminal identifier and a control code for activating second mobilecommunication network 20. Hereafter, control unit 510 operates theprocess (a second stand by for process) shown in a flowchart of FIG. 8(Step SA8). On the contrary, in a case that the determination result inStep SA5 is “No”, control unit 510 displays on display unit 520 thatmobile terminal 50 is outside a service area (Step SA9), and repeats theprocess after Step SA1.

In this embodiment, when mobile terminal 50 is turned on, mobileterminal 50 receives notification information, transmitted from basestation 21, by sufficiently electronic field intensity since mobileterminal 50 is in service area 210A (that is to say, around the centerof service area 100). Therefore, when the determination result in StepSA1 is “Yes”, control unit 510 executes the process from Step SA2 toStep SA4. A location registration message transmitted from mobileterminal 50 in Step SA2 is transmitted to location management device 12from base station 11, and location management device 12 that hasreceived a location registration message stores a terminal identifier incorrelation with location information, both of which are included in alocation registration message. On the other hand, an activation message,transmitted from mobile terminal 50 in Step SA3, is transmitted tomanagement device 60 from base station 11. Management device 60 that hasreceived an activation message activates first mobile communicationnetwork 10 on the basis of a control code included in the activationmessage. Specifically, management device 60 writes in registrationsection of a location registration management table (FIG. 4), “1” incorrelation with a terminal identifier included in an activationmessage.

In this embodiment, a location registration message and an activationmessage are transmitted to mobile terminal 50 separately; however, alocation registration message including a control code may betransmitted to mobile terminal 50. Specifically, when locationmanagement device 12 or 22, which has received a location registrationmessage including a control code, transmits an activation message tomanagement device 60, management device 60 activates a mobilecommunication network to which mobile terminal 50 is registered. Asdescribed above, mobile terminal 50 is able to use a mobilecommunication service through first mobile communication network 10since mobile terminal 50 is registered to first mobile communicationnetwork 10, and first mobile communication network 10 is activated.

<2. Operation at the Time When Mobile Terminal 50 Moves Outside ServiceArea 100>

Next, the operation of mobile terminal 50 will be described withreference to FIG. 7 when a user of mobile terminal 50 operating a firststand by for process in compliance with a flowchart in FIG. 7, movesfrom location registration area 210A to location registration area 210B(that is to say, moves outside service area 100).

Firstly, control unit 510 operated as shown in a flowchart in FIG. 7determines whether mobile terminal 50 is in service area 100 (Step SB1).In a case that the determination result in SB1 is “Yes”, control unit510 stands by for a call transmitted from first mobile communicationnetwork 10 (Step SB2), and repeats the process after Step SB1. On theother hand, in a case that the determination result in Step SB1 is “No”,control unit 510 executes the process from Step SA6 to SA8, registersmobile terminal 50 to second mobile communication network 20, andexecutes a second stand by for process.

In this embodiment, control unit 510 of mobile terminal 50 cannotreceive notification information transmitted from base station 21 sincelocation registration area 210B to which mobile terminal 50 moves islocated outside service area 100 as shown in FIG. 2. Therefore, controlunit 510 determines that mobile terminal 50 is outside service area 100,and the determination result in SB1 is “No”. Hereafter, control unit 510executes the process from Step SA6 to Step SA8. As described above,mobile terminal 50 is able to use a mobile communication service throughsecond mobile communication network 20 since registration area of mobileterminal 50 is changed to second mobile communication network 20, andsecond mobile communication network 20 is activated.

<3. Operation at the Time When Mobile Terminal 50 Moves From LocationRegistration Area 210B to 210A>

Next, the operation of mobile terminal 50 will be described withreference to FIG. 8 when a user of mobile terminal 50 operated as shownin a flowchart in FIG. 8, moves from location registration area 210B tolocation registration area 210A.

As shown in FIG. 8, control unit 510 determines whether a mobileterminal 50 user is calling through second mobile communication network20 (Step SC1), and repeats the Step SC1 process while the determinationresult in Step SC1 is “Yes”. This is because a call is disconnected ifthe location registration area of mobile terminal 50 is changed fromfirst mobile communication network 10 to second mobile communicationnetwork 20 while mobile terminal 50 is in use.

Then, control unit 510 determines whether the location registration areaof mobile terminal 50 is changed (Step SC2) in a case that thedetermination result in Step SCI is “No”. Specifically, control unit 510compares location information included in notification informationreceived through a second communication IF unit 542 with locationinformation stored in storing unit 550. Then, if location informationincluded in notification information is different from locationinformation stored in storing unit 550, control unit 510 determines thatthe location registration area of mobile terminal 50 is changed.

In a case that the determination result in Step SC2 is “No”, controlunit 510 executes the process of Step SC6. On the other hand, in a casethat the determination result in Step SC2 is “Yes”, control unit 510determines whether mobile terminal 50 can be registered to first mobilecommunication network 10 from the location registration area wheremobile terminal 50 is currently located, on the basis of registrationpossibility information included in notification information receivedthrough second communication IF unit 542 (Step SC3). Specifically,control unit 510 determines that mobile terminal 50 can be registered tofirst mobile communication network 10 in a case that registrationpossibility information is “01”, and mobile terminal 50 cannot beregistered to first mobile communication network 10 in a case thatregistration possibility information is

In this embodiment, location information stored in storing unit 550 ofmobile terminal 50 indicates location registration area 210B, andlocation information received through second communication IF unit 542indicates location registration area 210A; therefore, the determinationresult in Step SC2 is “Yes”. As a result, control unit 510 executes theprocess of Step SC3. And, since in this case registration possibilityinformation, included in notification information received throughsecond communication IF unit 542, is “01”, the determination result inStep SC3 is “Yes”.

In a case that the determination result in Step SC3 is “No”, controlunit 510 executes the process of Step SC6, and in a case that thedetermination result in Step SC3 is “Yes”, control unit 510 attempts toregister mobile terminal 50 to first mobile communication network 10(Step SC4). Specifically, control unit 510 receives notificationinformation, transmitted from base station 11, through firstcommunication IF unit 541, and attempts to register mobile terminal 50to first mobile communication network 10 by using location informationincluded in the received notification information. As described above,the process of Step SC4 is executed since the determination result inStep SC3 is “Yes”.

Next, control unit 510 determines whether mobile terminal 50 issuccessfully registered to first mobile communication network 10 (StepSC5), and executes the processes of Steps SA3 to SA4 in a case that thedetermination result in Step SC5 is “Yes”. On the other hand, in a casethat the determination result in Step SC5 is “No”, control unit 510stands by for a call from second mobile communication network 20 (StepSC6), and repeats the process after Step SC1. In this embodiment, sincemobile terminal 50 is successfully registered to first mobilecommunication network 10, mobile terminal 50 executes the process ofStep SA3 and SA4. Then, the location registration of mobile terminal 50is changed to first mobile communication network 10, and first mobilecommunication network 10 is activated. Consequently, mobile terminal 50is able to use a mobile communication service through first mobilecommunication network 10.

In this embodiment, it is described that control unit 510 attempts toregister mobile terminal 50 to first mobile communication network 10 onetime in a case that mobile terminal 50 can be registered to first mobilecommunication network 10 from a location registration area where mobileterminal 50 is currently located. However, a number of attempts toregister mobile terminal 50 to first mobile communication network 10 bycontrol unit 510 is not limited to one time, it is also possible thatcontrol unit 510 attempts location registration to first mobilecommunication network 10 a plurality of times (e.g. three times) atpredetermined intervals (e.g. five-minute intervals). That is to say, inthe present invention, the number of attempts to register mobileterminal 50 is not limited to one if a maximum number of attempts forlocation registration to first mobile communication network 10 is set.The reason for setting a maximum number of attempts is to avoidinterrupting communication through second mobile communication network20, and wasting power supply of mobile terminal 50.

<C. Modification>

The present invention is not limited to the embodiments described above,and may be modified within the scope of the invention. For example, thefollowing modifications are possible.

<Modification 1>

In the above embodiment, it is described that mobile terminal 50 isalways registered to first mobile communication network 10 by priority.However, mobile terminal 50 may be operated on the basis of one of thefollowing three operation modes selected by a user. The first operationmode is to register to first mobile communication network 10 bypriority. The second operation mode is to register only to first mobilecommunication network 10. The third mode is to register only to secondmobile communication network 20. For example, if the second operationmode is selected by a user, as shown in a flowchart of FIG. 6, controlunit 510 performs the process of only Step SA9 in a case that thedetermination result in Step SA1 is “No”. Then, in a flowchart of FIG.7, control unit 510 performs the process of only Step SA9 in place ofSteps SA 7 and 8 in a case that the determination result in Step SB1 is“No”.

<Modification 2>

In the above embodiment, it is described that a terminal identifier forspecifying mobile terminal 50 is pre-stored in storing unit 550.However, mobile terminal 50 can be provided with and use a removable UIM(User Identity Module) having a pre-stored terminal identifier.

<Modification 3>

In the above-described embodiment, it is described that each of basestation 21A and 21B transmits registration possibility information,which is 2-bit information having a bit pattern of either “00” or “01”.However, registration possibility information transmitted by basestation 21 belonging to second mobile communication network 20 is notlimited to the above 2-bit information having a bit pattern of either“00” or “01”. For example, base station 21 may transmit to mobileterminal 50, registration possibility information for registering mobileterminal 50 to first mobile communication network 10 after a long timeperiod, when base station 21 is located farther from the center ofservice area 100. Generally, the farther mobile terminal 50 is locatedfrom the center of service area 100, the more likely it is thatregistration to first mobile communication network 10 will fail.Accordingly, when mobile terminal 50 is located in second mobilecommunication network 20, it is preferable that the farther mobileterminal 50 is located from the center of service area 100, the longertime mobile terminal 50 should be in second mobile communication network20. Also, base station 21 belonging to a location registration area ofservice area 100 may transmit to mobile terminal 50, registrationpossibility information for limiting location registration to firstmobile communication network 10. The above examples are to limitlocation registration to first mobile communication network 10 for usinga voice communication service, or for using a packet communicationservice.

<Modification 4>

In the above-described embodiment, it is described that when mobileterminal 50 is registered to second mobile communication network 20,mobile terminal 50 attempts to register to first mobile communicationnetwork 10 whenever mobile terminal 50 moves from current locationregistration area to another location registration area. However, mobileterminal 50 attempts to register to first mobile communication network10 whenever mobile terminal 50 moves from current radio area to anotherradio area, or from a current sector to another sector within a currentradio area even when mobile terminal 50 is in the same radio area.Further, with regard to the case that mobile terminal 50 moves fromfirst mobile communication network 10 to second mobile communicationnetwork 20 after moving from second mobile communication network 20 tofirst mobile communication network 10, when mobile terminal 50 is stillin the same location registration area, mobile terminal 50 may notattempt to register to first mobile communication network 10 afterattempting more than a predetermined number of times. For example, inlocation registration area 210C of FIG. 9, when a user of a mobileterminal 50 moves back and forth between “point 1”(within service area100) and “point 2” (outside service area 100) several times, mobileterminal 50 is registered to first mobile communication network 10whenever the user moves to “point 1”. But, according to themodification, mobile terminal 50 is not registered to first mobilecommunication network 10 since mobile terminal 50 does not attempt to beregistered to first mobile communication network 10 after attemptingmore than a predetermined number of times, therefore, the inconvenienceis solved.

<Modification 5>

In the above embodiment, it is described that when mobile terminal 50 isregistered to first mobile communication network 10, first mobilecommunication network 10 is activated unconditionally. However, it ispossible that first mobile communication network 10 may only beregistered if a user of mobile terminal 50 is an authorized user.

<Modification 6>

In the above embodiment, it is described that mobile terminal 50 isregistered to either first mobile communication network 10 or secondmobile communication network 20, and stands by for a call. However, amobile communication service used by mobile terminal 50 is not limitedto voice communication, but may also be packet communication. Further,mobile terminal 50 may use both communication services at the same time.Then, in a case that mobile terminal 50 uses both communicationservices, mobile terminal 50 may be registered to first mobilecommunication network 10 from second mobile communication network 20only if location registration using voice communication and packetcommunication is performed successfully, or only if locationregistration using either voice communication or packet communication issuccessful. Further, when mobile terminal 50 belonging to second mobilecommunication network 20 performs packet communication, mobile terminal50 may be registered to first mobile communication network 10 fromsecond mobile communication network 20. This is because although amobile terminal 50 is moved to another mobile communication networkwhile performing packet communication, packet communication is notsusceptible to changing a location registration area of mobile terminal50 to another mobile communication network, as compared with a voicecommunication.

1. A mobile terminal comprising: a communication unit configured tocommunicate over a first mobile communication network and a secondmobile communication network; a control unit coupled with saidcommunication unit, said control unit operable to register said mobileterminal with said second mobile communication network only whenregistration with said first mobile communication network isunavailable; a memory coupled with said control unit, wherein saidcontrol unit is further operable to store location information in saidmemory, said location information comprising first location informationindicative of said first mobile communication network or second locationinformation indicative of said second mobile communication network; saidcommunication unit further operable to receive from said second mobilecommunication network notification information comprising said firstlocation information and a registration possibility indicationindicative that registration to said first mobile communication networkis possible; and said control unit further operable to compare saidfirst location information received in said notification information tolocation information stored in said memory and always register saidmobile terminal with said first communication network in response tosaid second location information being stored in said memory, and saidpossibility information being indicative that registration to said firstmobile communication network is possible.
 2. The mobile terminal ofclaim 1, wherein said control unit is further operable to register saidmobile terminal with said first mobile communication network only afterconfirmation that said mobile terminal is not calling through saidsecond mobile communication network.
 3. The mobile terminal of claim 1,wherein said control unit is further operable to store said firstlocation information in said memory in place of said second locationinformation upon registration with said first mobile communicationnetwork.
 4. The mobile terminal of claim 1, wherein said control unit isfurther operable to generate and transmit a first activation messageover said first mobile communication network for receipt by a managementdevice, and generate and transmit a second activation message over saidsecond mobile communication network for receipt by said managementdevice, wherein said management device is configured to store and updateinformation specifying a mobile communication network with which saidmobile terminal is currently activated to receive a call, based on saidfirst activation message and said second activation message.
 5. Themobile terminal of claim 4, wherein said control unit is furtheroperable to generate said first activation message after storage of saidsecond location in said memory, and generate said second activationmessage after storage of said first location information in said memory.6. The mobile terminal of claim 4, wherein said first activation messagecomprises an identifier of said mobile terminal and a first control codeto activate said first mobile communication network, and said secondactivation message comprises said identifier of said mobile terminal anda second control code to activate said second mobile communicationnetwork.
 7. The mobile terminal of claim 1, wherein said notificationinformation further comprises timing information indicative of a maximumnumber of attempts to register to said first mobile communicationnetwork, and said control unit is further operable to attempt toregister to said first mobile communication network a number of timesindicated with said timing information before registration with saidsecond mobile communication network.
 8. The mobile terminal of claim 7,wherein said notification information further comprises specification ofa predetermined interval of time between attempts to register to saidfirst mobile communication network, and said control unit is furtheroperable to attempt to register to said first mobile communicationnetwork at said predetermined interval of time.
 9. The mobile terminalof claim 1, wherein said communication unit is operable to communicatevoice communication and data communication, and said control unit isoperable to register with said first mobile communication network forvoice communication when said communication unit is currently engaged ina data communication over said second mobile communication network. 10.The mobile terminal of claim 1, wherein said mobile terminal is onlyregisterable with said first mobile communication network when a user ofsaid mobile terminal is an authorized user of said first mobilecommunication network.
 11. The mobile terminal of claim 1, wherein saidregistration possibility information comprises a limitation ofregistration with said first mobile communication network to only one ofvoice communication or data communication.
 12. The mobile terminal ofclaim 1, wherein said first mobile communication network and said secondmobile communication network are divided into a plurality ofregistration areas, and receipt from said second mobile communicationnetwork of notification information comprising said first locationinformation and said registration possibility indication indicative thatregistration to said first mobile communication network is possible is aresult of a change of location of said mobile terminal from oneregistration area to another registration area.
 13. The mobile terminalof claim 1, wherein said first mobile communication network and saidsecond mobile communication network are divided into a plurality ofradio areas, and receipt from said second mobile communication networkof notification information comprising said first location informationand said registration possibility indication indicative thatregistration to said first mobile communication network is possible is aresult of a change from a current radio area to another radio area. 14.The mobile terminal of claim 1, wherein said first mobile communicationnetwork and said second mobile communication network are divided into aplurality of radio areas each comprising a plurality of sectors, andreceipt from said second mobile communication network of notificationinformation comprising said first location information and saidregistration possibility indication indicative that registration to saidfirst mobile communication network is possible is a result of a changefrom a current sector to a new sector within a radio area.
 15. Alocation registration changing method comprising: registering a mobileterminal with a second mobile communication network in response toregistration with a first mobile communication network beingunavailable; storing second location information of said second mobilecommunication network in a memory of said mobile terminal when saidmobile terminal is registered to said second mobile communicationnetwork; receiving, with said mobile terminal over said second mobilecommunication network, notification information that includes firstlocation information of said first mobile communication network andregistration possibility information that includes an indication ofwhether registration to said first mobile communication network isavailable; said mobile terminal sensing a change in location of saidmobile terminal; said mobile terminal comparing said second locationinformation stored in said memory with said first location informationreceived in said notification information; said mobile terminal,responsive to said first location information and said second locationinformation being different, checking said registration possibilityinformation to confirm registration to said first mobile communicationnetwork is available; and said mobile terminal attempting to registersaid mobile terminal to said first mobile communication network inresponse to confirmation by said mobile terminal that said registrationpossibility information indicates registration to said first mobilecommunication network is available.
 16. The method of claim 15, whereinsaid mobile terminal sensing a change in location of said mobileterminal comprises confirming that said mobile terminal is not callingthrough said second mobile communication network, and delaying sensing achange in location of said mobile terminal when said mobile terminal iscurrently calling through said second mobile communication network. 17.The method of claim 15, wherein said mobile terminal attempting toregister said mobile terminal to said first mobile communication networkcomprises said mobile terminal transmitting a location registrationmessage over said first mobile communication network to a locationmanagement device in said first mobile communication network to registerin said first mobile communication network, and said mobile terminaltransmitting a notification message over said first mobile communicationnetwork to a management device in communication with both said firstmobile communication network and said second mobile communicationnetwork, said notification message indicative that registration has beensuccessfully changed to said first mobile communication network.
 18. Themethod of claim 17, wherein said mobile terminal transmitting a locationregistration message comprises transmitting a mobile terminal identifierand location information of said mobile terminal to said locationmanagement device, and transmitting a notification message comprisestransmitting a terminal identifier of said mobile terminal and a controlcode to activate said first mobile communication network to saidmanagement device.
 19. The method of claim 15, wherein receiving, withsaid mobile terminal over said second mobile communication network,registration possibility information comprises storing said registrationpossibility information in a memory included in said mobile terminal,and checking said registration possibility information comprisesaccessing said registration possibility information stored in saidmemory.
 20. The method of claim 15, wherein registering a mobileterminal with a second mobile communication network in response toregistration with a first mobile communication network being unavailablecomprises first attempting to register with said first mobilecommunication network and then registering with said second mobilecommunication network.
 21. A communication system comprising: a firstmobile communication network that includes a first location managementdevice, wherein said first location management device is operable tomanage location information received from any of a plurality of mobileterminals that choose to register to said first mobile communicationnetwork; a second mobile communication network that includes a secondlocation management device and a base station, said second locationmanagement device operable to manage location information received fromany of said mobile terminals that choose to register to said secondmobile communication network, and said base station positioned withinsaid first mobile communication network, wherein said base station isoperable to transmit, for receipt by any of said mobile terminals thatare registered to said second mobile communication network, registrationpossibility information indicative that registration to said firstmobile communication network is possible; and a management devicecoupled with said first mobile communication network and said secondmobile communication network, said management device operable to storelocation registration data correlated with a respective mobile terminalidentifier for each of said mobile terminals, said management devicefurther operable to update said location registration data in responseto receipt from any one of said mobile terminals of a notificationmessage generated and transmitted with said respective any one of saidmobile terminals, wherein said notification message is indicative thatsaid respective any one of said mobile terminals completed registrationto one of said first mobile communication network or said second mobilecommunication network and stands by for a call.
 22. The communicationsystem of claim 21, wherein said management device is operable to storesaid location registration data correlated with a mobile terminalidentifier in a management table.
 23. The communication system of claim21, wherein said management device is operable, in response to a requestrelated to a specified mobile terminal, to specify a mobilecommunication network to which said specified mobile terminal isregistered based on said stored location registration data correlatedwith a mobile terminal identifier.
 24. The communication system of claim21, wherein said management device is operable to receive data from saidfirst mobile communication network when said notification is from afirst mobile terminal registered with said first mobile communicationnetwork, and said management device is operable to receive data fromsaid second mobile communication network when said notification is froma second mobile terminal registered with said second mobilecommunication network.
 25. The communication system of claim 21, whereinsaid notification message and said location information are differenttransmissions from said mobile terminal.